1. Field of the Invention
The present invention relates to a method of determining a photo mask, a method of manufacturing a semiconductor device, and a computer program product.
2. Description of the Related Art
With the reduced sizes and increased integration levels of semiconductor devices, it has been more and more important to accurately form patterns with desired sizes. However, with pattern miniaturization, an optical proximity effect (OPE) prevents patterns with desired shapes from being faithfully formed. Thus, for actual photo masks, optical proximity correction (OPC) is performed on the mask patterns so as to obtain patterns with desired shapes (see, for example, Jpn. Pat. Appln. KOKAI Publication No. 9-319067).
The optical proximity effect generally depends on the characteristics of an exposure apparatus. This varies the optical proximity effect among exposure apparatuses. Thus, a photo mask subjected to appropriate optical proximity corrections for a certain exposure apparatus may fail to provide a pattern with a desired shape for a different exposure apparatus. To obtain a pattern with the desired shape, it is necessary to newly produce a photo mask subjected to optical proximity correction suitable for the different exposure apparatus. However, production of a new photo mask extends a manufacture period. Adjustment of an exposure parameter (for example, illumination shape) for the different exposure apparatus enables proper exposure to be achieved without producing a new photo mask. That is, provided that the adjustment of the exposure parameter results in a pattern meeting a predetermined condition, a new photo mask need not be produced even if the exposure apparatus is changed.
However, the adjustment of the exposure parameter is limited and thus does not always result in a pattern meeting the predetermined condition. If the adjustment of the exposure parameter does not result in a pattern meeting the predetermined condition, then a new photo mask must be produced. An operation for adjusting the exposure parameter is performed through a trial and error process at a manufacture site such as a factory. If the adjustment operation does not result in a pattern meeting the predetermined condition, the time spent in the adjustment operation will be wasteful. This further extends the manufacture period.
Thus, two measures, production of a new photo mask and adjustment of the exposure parameter, are possible if the exposure apparatus is changed. However, the lack of definite criteria for determining which measure to take results in extension of the manufacture period. It is therefore important to make an early and appropriate determination for measures to be taken if the exposure apparatus is changed.